Ultra-high temperature ceramic composites are particularly useful for application in aggressive environments in which ultra-high temperatures approaching or exceeding 3000° C. and complex ablation dynamics activate mechanical and chemical degradation. Some examples of the use of these thermal protection systems in hypersonic vehicles and re-entry vehicles include the use thereof in leading edges, nosecones, rocket nozzles, and exhaust cones.
Transition metal-carbide ceramics are known for showing the highest melting points of most ceramic materials. Furthermore, hybridised (multi-phased) matrices allow the constituent components to show complementary behaviour in resisting ablative degradation when in service. However, the prevalence of such hybridised matrix composites especially with all-carbides ceramic matrices is still limited.
Carbon fibre reinforced carbon matrix (Cf/C) composites succumb to oxidation at temperatures as low as 500° C. when in service, and hence rapidly degrade in effectiveness. The carbon matrix's ablative resistance can be upgraded by introducing transition metals, which can be processed to form carbides, nitrides and borides with high melting points. The usefulness of the substituting transition metal ceramics is ultimately proved in an oxidative environment, whereby the temperature at which the formed oxides melt and volatize determines the degree of protection it imparts to the Cf/C composite.
EP 1 157 979 describes how to impregnate metal silicides into a C/C composite at temperatures around the melting point of the metal silicide, and discloses the infiltration of a metal silicide into a Si—SiC gradient-based or a C/C based composite. Furthermore, in the patent the metal silicide(s) is (are) infiltrated successively. No consequential reaction of the transition metal infiltrants with the carbon matrix is mentioned.
US Patent Publication no. 2004/207133 embodies the formation of a single transition metal carbide matrix. Metal carbide is formed first, with Si then diffused into the formed carbides matrix. A metal oxide coating, particularly like ZrO2, formed around the carbon fibres is proposed, having been introduced by chemical vapour infiltration. Chemical vapour infiltration was performed again to introduce a carbon matrix on top of the coating, serving as the matrix which embeds the coated fibres. Zr was then reaction infiltrated in molten state into the C/C composite at about 1950° C. and molten Si subsequently diffused at about 1500° C. Infiltration of the metal and or silicon was realized by placing pieces thereof above the C/C composite, so as to infiltrate downwards into the latter material. Infiltration was proposed to be done typically at 25-100° C. above the melting point of the metal of the silicon in an induction graphite furnace with long heating and cooling times. The additional infiltration of C before Si infiltration was also proposed. MC and SiC typically occupy 30-60 vol. % in the composite.
International PCT patent application no. PCT/FR2010/051012 is based on vanadium and vanadium alloys and utilises a self-healing protection mechanism for service temperatures up to 900° C. when combined with vitreous oxides, e.g. formed from B4C.
U.S. Pat. No. 5,965,266 presents the use of self-healing SiC based protection directly on the C/C composite. Protection is limited to application temperatures way below the required ultra-high temperature mark of 3000° C.
Ultra-high temperature ceramics are usually intended to operate at temperatures above 2000° C., and preferably above 3000° C. For the most part the prior art has focused on multi-layered interphases and coatings (for example those disclosed in U.S. Pat. No. 6,869,701) in protecting the composite reinforcement skeleton. US Patent Publication no. 2014/0363663 is an example of a composite utilizing both a multi-layered ceramic matrix and fibre coating to reduce oxidation in the composite. The ceramic multi-layers enable the operation of a crack deflection mechanism that provides a tortuous path that delays oxygen transport into the composite.
However, to date no ultra-high temperature ceramic composite has been reported to satisfactorily withstand in-service temperatures of 3000° C., or more, for a satisfactory amount of time.
It is therefore an object of the present invention to provide an improved ultra-high temperature ceramic composite which addresses the shortcomings experienced in the art, including addressing the phenomenon of in-situ matrix cracking.